The present invention relates in general to a transmission control apparatus and, more specifically, to commercial utility vehicles equipped with a manual transmission which varies the speed in stages, although the invention also offers advantages for such commercial vehicles that are equipped with automatic transmissions.
With automatic transmissions, auxiliary shifts or shift commands are being increasingly used in today's commercial motor vehicles. The required shift signals for these automatic transmissions are determined primarily on the basis of various conditions inside the vehicle. In hilly areas of a country, in particular, there are a number of increased problems associated with producing meaningful shift signals for such transmissions, and such problems are most specifically encountered on changing road grades.
When, for example, a vehicle is travelling uphill over the crest of a hill, it is possible then, because of the decreasing slope, that the vehicle will continue to accelerate with the same amount of drive power. Furthermore, on account of the increasing speed of the motor, a criterion for shifting the transmission into a higher gear will soon be reached. But, in such a situation, it may be inappropriate to shift to the higher gear, because behind the crest of the hill there will normally be a descending slope, and then the new higher gear may be inappropriate on account of excessive speed, and the transmission must then be downshifted in such commercial vehicles to obtain the braking effect of the motor.
Quite similar problems will likewise occur when a commercial vehicle is travelling downward over the crest of a hill. Here too, is a situation where it would be inappropriate to shift the transmission into a higher gear, as long as the slope continues to increase, because again, the beneficial braking effect of the motor would thereby be decreased.
If, for example, the vehicle is travelling through a valley, than, when reaching a downhill grade, it is also inappropriate to shift the transmission too soon to a higher gear, because the driver will usually want to take advantage of the power of the motor to attain even higher speeds to gain some additional momentum for climbing the subsequent hill. Specifically too when an uphill stretch of a valley is being negotiated it is important not to shift the transmission to a higher gear prematurely because the slope of the roadway can become so great that the required drive torque cannot, at a somewhat later point, be brought into a higher gear and then it will become necessary for the driver to downshift the transmission once again.
The present invention teaches an apparatus to automatically determine and control an appropriate shift point in an over-the-road vehicle transmission control mechanism. The shift point control apparatus comprises a differentiating means connected to the transmission control mechanism for substantially continuously determining a difference in a constant speed drive torque on such vehicle motor and for generating a signal value that is representative of a difference in the constant speed drive torque of such vehicle motor.
A comparator means is provided which is connected to receive the signal value representative of a difference in the constant speed drive torque for comparing this signal value with a predetermined value to determine both an increasing gradient and a decreasing gradient in a roadway and for generating at least one of a positive and a negative signal value that will be representative of an increasing gradient and an opposite sign signal value that will be representative of a decreasing gradient.
A verifying means is also provided which is connected to the transmission control mechanism for verifying the increasing and decreasing roadway gradients.